Induction-motor.



No. 732,153. PATENTED JUNE so, 1903. U A. E. AVERRETT.

INDUCTION MOTOR.

APPLICATION FILED APR. 21, 1903.

H0 MODEL.

- 'xruzy UNITED STATES Patented June 30, 1903.

PATENT OFFICE.

ANDREW E. AVERRETT, OF SCHENEOTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

INDUCTION-MOTOR.

SPECIFICATION forming part of Letters Patent No. 732,153, dated June 30, 1903.

Application filed April 21,1903- Serial No. 153.588- (No model.)

To all whom it may concern:

Be it known that I, ANDREW E. AVERRETT, a citizen of the United States, residing at Schenectady, in the county of Schenectady and State of New York, have invented certain new and useful Improvements in Induction-Motors, of which the following isa specification.

My invention relates to induction-motors, and has for its object the production of an induction-motor having efficient and economical starting means.

In startinginduction-motors a tremendous rush of current due to the great slip causes the secondary poles to overpower those of the primary member and gives the motor a low starting torque. In order to prevent this'objectionable result, it is common practice to provide a resistance in circuit with the secondary winding which is gradually cut out as the motor speeds up; but the employment of such starting means necessitates the use of switching connections and sliding contacts, which are more or less complicated and 0bjectionable. I avoid these complications and objections and attain the desired starting torque by making a portion of the secondary winding of iron. In the squirrel-cage armature shown in the accompanying drawings this member takes the form of iron end rings, which replace the usual copper end rings and electrically connect the longitudinal conductor-bars. By the use of these iron end rings I obtain the desired high resistance in the secondary Winding at starting and a gradual reduction of resistance as the motor speeds up, because of the large skin effect in iron when used as a conductor for alter nating currents. This skin effect or tendency of an alternating current to avoid the central portions of solid conductors and to flow or pass mostly through the superficial portions in the case of iron produces a very great increase of impedance over the normal resistance-that is, a very great increase of opposition to the current flow. Tests made with The skin effect is also dependent upon the frequency of the current passing through the conductor and is greatest when the frequency is highest.

From this it follows that the impedance of said winding is the greatest, and it also follows that the impedance gradually decreases as the motor speeds up and approaches synchronism.

In the accompanying drawings, in which like characters refer to like parts, I have illustrated an induction armature of the squirrel-cage type constructed in accordance with my invention.

In the drawings, Figure 1 is an end View of the armature with a portion of the end ring broken away. Fig. 2 is a sectional view on the line 2 2 of Fig. 1; and Fig. 3 is an enlarged sectional view, similar to Fig. 2, of a portion of the armature.

The armature consists, essentially, of a spider 10, keyed to the shaft 11 and supporting at its exterior a laminated structure 12, clamped between end rings 13 through the agency of bolts 14. Thelaminated structure 12 is composed of sheet-metal punchings provided with suitable apertures for the recepa tion of longitudinal copper conductor-bars 15. These conductor-bars are bolted at their opposite ends to iron rings 16, which are engaged by small supporting-lugs 17 on the clamping-rings 13. The clamping-rings are provided with blades 18, which are adapted to create a current of air for cooling the armature when in operation.

The construction here described is identical with that in .common use except that the longitudinal conductors 15 are secured to iron end rings 16 instead of to copper rings, as heretofore.

7 From the above it is apparent that the current induced in the bars 15 will necessarily flow through portions of the iron ring during the rotation of the armature.

In view of the explanation at the beginning of this description it is thought that the operation will be clear.

What I claim as new, and desire to secure I 3. In an inductionmotor armature, the by Letters Patent of the United States, iscombination of an iron core, longitudinal cop- 1. In an induction motor armature, the l per bars embedded in said core, and iron end combination of a core composed of magnetic rings mechanically and electrically connect- I5 5 material, and a winding on said core, part of ing said bars.

which is iron and part copper. In witness whereof I have hereunto set my 2. In an induction-motor armature, the hand this 20th day of April, 1903. combination of a core composed of magnetic material,copper conductors extendinglength- 1o wise of said core, and iron end members electrically connecting said conductors.

ANDREW E. AVERRETT. I/Vitnesses:

EDWARD WILLIAMS, J12, MARCUS L. BYNG, 

